This invention generally relates to techniques and devices for providing electrical power to electronic components. More particularly, various aspects of the invention relate to digitally controlling a modular power supply such as a power supply incorporating one or more voltage regulator modules.
As electronic components become increasingly powerful, fast and complex, such devices require increasingly capable power supplies. Many devices such as microprocessors, microcontrollers and the like now demand that relatively high current levels be provided extremely efficiently and with very low fluctuations in current and voltage. Microprocessors such as those available from the Intel Corp. and Motorola Inc., for example, can demand a continuous supply of current in excess of 100 amperes at voltage levels below 2 volts.
Conventional power supplies for use in microprocessor systems typically include switched-mode power supplies such as voltage regulator modules (VRMs) or the like operating in a voltage-controlled mode. Each VRM typically controls a voltage across the output load using conventional feedback and compensation circuitry. In such embodiments, the voltage across the load is sensed and compared against a reference signal in the feedback path. The compensation circuitry then controls a gating signal that determines the output voltage as appropriate to provide electrical power to the load component.
To implement the power supply, a conventional VRM is frequently configured as a conventional step-down buck converter. A DC load line is often specified for microprocessor loads such that the output load voltage decreases with increasing load current. The scheme of dynamically adjusting the output voltage with load current is commonly referred to as active voltage positioning (AVP).
Conventional single-stage buck converters, however, typically do not provide adequate power for many applications due to thermal constraints and efficiency requirements. To overcome this issue, the power supply modules are typically configured as multi-phase converters such that several phase-separated buck channels operate in parallel within the VRM so that load current is appropriately distributed between the various stages. The multiple channels allow for multiphase switching within the power stage to reduce thermal stress, to reduce output ripple voltage and to improve the ability to finely control the electrical output characteristics of the module.
In cases where the current consumed by the load is higher than that provided by a single module, multiple modules may be connected in parallel to supply a greater amount of current. Two or more voltage regulator modules (VRMs) may be used to supply power to a conventional dual microprocessor chip set, for example. Modular power supplies typically exhibit the added benefits of redundancy and improved thermal response, as well as improved design flexibility.
To provide tight voltage regulation and to minimize thermal overstress, it is frequently desired to evenly balance the current provided between the individual channels of the VRM, as well as the current provided between parallel-connected VRMs. To balance the currents provided by the multiple modules and channels, some information about the currents provided within the system may be required. Several analog current sensing methods are known for conventional power supplies. Some exemplary current sensing schemes include: (i) measuring voltage across a sense resistor placed in series with the input voltage, (ii) measuring voltage across a low-side FET in a buck stage, (iii) measuring voltage across an output inductor, and (iv) using a current sense loop. Each of these schemes has drawbacks in the form of power loss, thermal drift, size and/or inaccuracy. Further, analog current sensing typically requires routing low magnitude current sense signals over a circuit board, which can be prone to noise pick-up because of the large-signal power stage activity. As a result, obtaining an accurate DC load line using analog controllers can be difficult in practice. An example of a conventional analog current management technique is shown in Intersil Technical Brief TB385 xe2x80x9cCurrent Sharing Technique for VRMsxe2x80x9d dated May 2000 and incorporated herein by reference.
Although various current control techniques have been attempted, none have effectively provided a reliable digital control technique suitable for next-generation modular power supplies. It is therefore desirable to produce a system and method for effectively managing and controlling currents provided in a modular power supply.
Systems, devices and methods for accomplishing a range of functions in a digitally controlled power converter are described. In an exemplary embodiment, currents flowing in the various channels are suitably converted to digital equivalents that can be processed to implement sharing between channels or between various modules. By monitoring the current provided on each channel, for example, a controller can determine an average current for the channels, which in turn can be used to identify and compensate for over- or under-production in any particular channel. Active voltage positioning techniques and overload protection may also be implemented using digital techniques.
According to a further exemplary embodiment incorporating inter-module current sharing, multiple voltage regulator modulators are suitably interconnected by a common ISHARE bus providing a density-modulated indication of the total amount of current being produced by the system. Each module provides a stream of pulses on the ISHARE bus such that the number of pulses provided within a set period of time is proportional to the total amount of current being produced by the module. By monitoring the total number of pulses present on the ISHARE bus, each module can become aware of the total amount of current produced within the system and can adjust its current output accordingly. Additionally, each module may incorporate active voltage positioning (AVP) techniques using digital feedback such that voltage and current are suitably controlled within each channel of each module.
Additional features of the present invention are brought out in the following detailed description of exemplary embodiments.